The present invention relates to a process and an arrangement for control of an automated gearbox.
The present invention relates to control of an automated gearbox, meaning a mechanical gearbox, which incorporates one or more constituent gearboxes, such as split, main and range gearboxes, and which is servo-assisted for the performance of gearchange movements. Such a gearbox usually forms part, together with a mechanical clutch (e.g. of plate type), of the driveline for a heavy vehicle driven by combustion engine.
xe2x80x9cKickdownxe2x80x9d is conventional term for pressing the accelerator pedal down sharply to or nearly to the full extent, whereby the driver indicates a desire for rapid accleration of the vehicle. In vehicles with automatic gearboxes, kickdown also usually involves changing down so that the engine speed can be adapted to a speed range in which the torque delivered by the engine is as great as possible. To this end, the vehicle""s accelerator pedal often incorporates a special sensor (xe2x80x9ckickdown sensorxe2x80x9d) which detects its sharply depressed position. The resulting increased gas mobilization causes a momentary engine speed increase simultaneously with a changedown to cater for a temporary vehicle speed increase. According to the state of the art, kickdown involves vhanging down by one or more gears to achieve the desired increase in torque and hence increase in the speed of the vehicle.
However, a process according to the state of the art entails the risk that a less efficient changedown may be initiated, resulting in a smaller vehicle speed increase than might be achieved on the basis of the vehicle""s performance.
An object of the present invention is to indicate a development of the state of the art whereby the present problems of the state of the art are eliminated.
This object is achieved by a process and an arrangement for the control of an automated gearbox which operates by determining possible gear combinations for changedown, calculating the acceleration for each combination, and changing to the combination which results in the shortest acceleration time.
The result is the selection of a gear combination which produces for each operating situation the shortest resultant acceleration time, meaning the shortest time to achieving a desired vehicle speed increase. To this end, the relationship for each gear combination between the engine speed/vehicle speed and the maximum drive power is stored in a memory to make it possible for the accelerative drive force Facc to be determined for each operating point for each vehicle combination. This and other operating parameters thus provide the basis for selecting the gear combination which produces the shortest acceleration time, resulting in optimisation of the kickdown function, an optimisation which may differ markedly from the more routine changedown achieved according to the state of the art.
The calculation of the accelerative force involves deriving values from the control system with regard to the maximum engine torque for the current engine speed. This entails taking the engine""s characteristics into account.
The kickdown function may be further refined according to one embodiment of the invention whereby the gearchange times for the various gear combinations are determined and preferably stored in a memory and this information is incorporated in the calculation of the shortest acceleration time. In, for example, gearboxes composed of two or more constituent gearboxes (e.g. main, split and range gearboxes), gearchange times do in fact depend entirely on whether the gearchange is to take place in only one constituent gearbox or in two or three of them. As certain gear changes can only be effected sequentially, changing gear in two or more constituent gearboxes entails a relatively long time for changing gear in the gearbox as a whole, i.e. a long period of time during which the driveline is broken.
Another embodiment of the invention involves the running resistance and/or the weight of the vehicle being calculated during its operation so that the relevant calculation data are constantly available.
The invention also relates to an arrangement for control of an automated gearbox whereby corresponding advantages are achieved as in the aforesaid process.
Further advantages will be evident from the following detailed description.